Oscillations or cycling discharges of neurons provide a clock or impose a "tempo" for various kinds of information processing. We recently found that olfactory bulb ET cells are endowed with spontaneous rhythmic bursting that persists and becomes more regular in the presence of fast synaptic blockers. Using simultaneous whole-cell recording from pairs of juxtaglomerular (JG) neurons, we were the first to discover that membrane potential oscillations and spontaneous bursting activity are highly correlated in external tufted (ET) cells associated with the same glomeruli. This synchronous activity occurs at theta frequency (1-8 Hz), the same frequency that characterizes investigative sniffing in rodents. Therefore, synchronous ET cell bursting may play an important role in olfactory coding and in regulating the induction of synaptic plasticity at the first input stage of the main olfactory bulb. In this proposal, we hypothesize that ET cells coordinate the activity of other olfactory bulb neurons and may play a role of a pattern generator of the olfactory bulb network. In particular, this project will assess the functional roles of synaptic and non-synaptic interactions in establishing correlated activity between ET cells and other neurons including interneurons and output neurons. We will use dual patch clamp and extracellular recording techniques and cross-correlation analysis to test the following hypotheses: (i) ET cell bursting activity is shaped by feedback dendrodendritic inhibition from PG cells, (ii) ET cells in neighboring glomeruli have correlated activity that is mediated by short axon cells, (iii) ET cells coordinate the activity of other output neurons, tufted and mitral cells, via chemical and electrical synapses. Taken together, the experiments proposed in this study will provide important, new insights into the intrinsic synaptic organization of the glomeruli and the role of glomerular circuitry in olfactory coding.